Increased halogenated tyrosine levels are useful markers of human skin ageing, reflecting proteins denatured by past skin inflammation

Summary Background. Photoageing of skin is thought to be caused by protein denaturation, which can be induced by ultraviolet radiation. Previous studies have also reported that inflammation is related to protein denaturation; however, the influence of inflammation on skin ageing has not been explored in detail. Aim. To investigate the possible connection between inflammation and protein denaturation, which might lead to skin ageing, we focused on halogenated tyrosine as a denatured substance produced during the inflammation process. Methods. We measured halogenated tyrosine in aged human skin. Inflammatory cells and halogenated tyrosine were detected by immunohistochemistry using antibodies to mast‐cell tryptase, neutrophilic myeloperoxidase and halogenated tyrosine. Finally, using elastic van Gieson (EVG) staining, we investigated whether the sites of halogenated tyrosine coincided with the sites at which proteins were denatured. Results. Immunohistochemical analysis indicated that both inflammatory cells and halogenated tyrosines increased with ageing in both photoexposed and photoprotected skin. EVG staining confirmed that the localization of halogenated tyrosine was close to the sites at which protein was denatured. Conclusions. Our investigations indicate a possible connection between skin ageing and inflammation, suggesting that halogenated tyrosine could be a useful marker of ageing skin.